U.S. patent number 4,655,210 [Application Number 06/819,686] was granted by the patent office on 1987-04-07 for foam bandage.
This patent grant is currently assigned to Seton Company. Invention is credited to Martin I. Edenbaum, Borys Rybalka.
United States Patent |
4,655,210 |
Edenbaum , et al. |
April 7, 1987 |
Foam bandage
Abstract
A disposable bandage, and a process for manufacturing it, which
is prepared from a single sheet or strip of liquid permeable,
flexible thermoplastic hydrophilic foam. The process includes
coating the entire surface of one side of a foam sheet or strip
with a layer of porous pressure sensitive adhesive, positioning
wound release material in the area of the sheet or strip intended
for wound contact, covering the same side of the laminate with a
suitable release liner and heat compressing the laminate except at
the locus of the wound release material. The foam bandage so
produced includes both a resilient absorbent pad and thin but
absorbent adhesive-coated tabs. Optionally, the bandage may have a
moisture vapor permeable, moisture impermeable skin thereon, to
provide a water- and bacteria-proof protective outer layer for the
foam bandage.
Inventors: |
Edenbaum; Martin I. (Princeton
Junction, NJ), Rybalka; Borys (Philadelphia, PA) |
Assignee: |
Seton Company (Newark,
NJ)
|
Family
ID: |
25228778 |
Appl.
No.: |
06/819,686 |
Filed: |
January 17, 1986 |
Current U.S.
Class: |
602/46;
602/900 |
Current CPC
Class: |
A61F
13/0203 (20130101); A61F 13/023 (20130101); A61L
15/425 (20130101); A61F 2013/0074 (20130101); Y10S
602/90 (20130101); A61F 2013/00868 (20130101); A61F
2013/00765 (20130101) |
Current International
Class: |
A61F
13/02 (20060101); A61L 15/42 (20060101); A61L
15/16 (20060101); A61F 13/00 (20060101); A61L
015/00 () |
Field of
Search: |
;128/156 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: McNeil; Gregory E.
Attorney, Agent or Firm: Webb, Burden, Robinson &
Webb
Claims
We claim:
1. A foam bandage, comprising a laminate having a liquid permeable
foam layer and a liquid permeable porous pressure sensitive
adhesive layer, and having a wound release material adjacent said
adhesive for separating said adhesive from a tissue healing area,
and securement means associated with said laminate to attach the
laminate.
2. The foam bandage according to claim 1, wherein said area of said
laminate intended for wound contact defines a pad.
3. The foam bandage according to claim 2, wherein said foam layer
and said adjacent porous pressure sensitive adhesive layer
exclusive of said pad are heat compressed laminates having a
thickness less than said pad.
4. The foam bandage according to claim 3, wherein said porous
pressure sensitive adhesive layer is permeable to liquid water and
serum.
5. The foam bandage according to claim 3, wherein said foam layer
is a thermoplastic polyurethane foam.
6. The foam bandage according to claim 5, wherein said
thermoplastic polyurethane foam is hydrophilic.
7. The foam bandage according to claim 6, wherein said hydrophilic
thermoplastic polyurethane foam has a moisture vapor permeable,
moisture impermeable skin thereon opposite said adhesive layer.
8. The foam bandage according to claim 7, wherein said moisture
vapor permeable, moisture impermeable skin is a urethane skin.
9. The foam bandage according to claim 4, wherein said wound
release material is permeable to liquid water and serum.
10. The foam bandage according to claim 9, wherein said porous
pressure sensitive adhesive layer is at least partially covered
with a release liner.
11. The foam bandage according to claim 10, wherein an absorbent
layer is positioned between said porous pressure sensitive adhesive
layer and said wound release material.
12. The foam bandage according to claim 11, wherein said porous
pressure sensitive adhesive layer and said wound release material
are each entirely covered with a release liner.
13. A method for preparing a foam bandage, comprising:
(a) selecting a low density liquid permeable foam sheet;
(b) adhering a porous pressure sensitive adhesive layer, which is
permeable to liquid water and serum, to said low density foam sheet
to form a laminate;
(c) positioning a wound release material in the area of said
laminate intended for wound contact to separate the adhesive from a
tissue healing area; and
(d) heat compressing the entire sheet thus produced except in the
area of said wound release material.
14. The method according to claim 13, wherein step (a) further
comprises the step of:
(a) selecting a low density foam sheet having a moisture vapor
permeable, moisture impermeable skin thereon.
15. The method according to claim 13, wherein step (a) further
comprises the step of:
(a) selecting a low density hydrophilic thermoplastic polyurethane
foam sheet having a moisture vapor permeable, moisture impermeable
urethane skin thereon.
16. The method according to claim 13, wherein step (c) further
comprises the step of:
(c) partially covering the area of said laminate intended for wound
contact with an absorbent material, positioning a wound release
material over the entire area of said laminate intended for wound
contact, and positioning a release layer adjacent said wound
release material.
17. The foam bandage according to claim 1, wherein said securement
means comprises said adhesive.
18. The foam bandage according to claim 1, wherein said foam is at
least partially open-celled.
19. The method according to claim 13, said foam being at least
partially open-celled.
Description
FIELD OF THE INVENTION
The present invention relates to disposable bandages for both minor
and major skin wounds and irritations and, more particularly,
relates to disposable bandages prepared from a single sheet of
polyurethane foam.
BACKGROUND OF THE INVENTION
Over-the-counter disposable bandages have enjoyed popularity for
decades. The use of such bandages is widespread in the first-aid
treatment of minor skin wounds such as abrasions and accidental
incisions. Moreover, certain features have been added to these
bandages, during their development, to increase comfort to the
user; these features include wound release materials, perforations
in the adhesive tabs, and the like. The resulting products have
gained substantial consumer acceptance.
Unfortunately, these disposable bandages continue to present
disadvantages both to the manufacturer and the consumer. The most
popular bandages include a perforated plastic sheet or strip, the
sides of which are ordinarily coated with a perforate pressure
sensitive adhesive composition on their inner surfaces, having a
wound covering pad (typically gauze) positioned in and adhered to
the center of the strip or sheet. The wound facing surface of the
pad is treated or laminated so as to prevent the pad from adhering
to the wound. Release material coated strips are placed over the
adhesive tabs and the bandage itself is then packaged and
sterilized for sale or use. This process, although it results in a
commercially acceptable product, requires several manufacturing
steps and a number of component materials, thus preventing the
simple, low-cost manufacture of the article.
Although the difficulties in manufacturing these bandages are
substantial, the most significant disadvantages are those to the
ultimate user of the bandage. Because the gauze pads lint, they
deposit dust and/or fiber into the open wound. The gauze pad itself
has so little thickness, compounded by a total lack of resilience,
that the pad provides to the wound site little if any protection
from contusion or other pressure trauma. This same gauze pad is
likewise deficient in that it can absorb and hold only small
amounts of medicaments or fluids such as wound exudates. In
addition, despite improvements in pressure sensitive adhesives in
recent years, conventional disposable bandages continue to cause
pain and tissue trauma upon removal, particularly in sensitive
areas such as the interdigital skin of the hands. Finally, the
overwhelming majority of these disposable bandages are used on the
fingers. When the adhesive tabs of these bandages are wrapped and
overlapped about a finger, the tabs lose most or all of their
moisture vapor permeability because the perforations in the
overlapping tabs seldom if ever align to permit moisture vapor
transmission. As a result, the skin covered by overlapping adhesive
tabs macerates beneath a plastic vapor barrier.
Even the most recent developments in the disposable bandage art
have failed to rectify the most significant of these problems. For
example, the "Unitary Adhesive Bandage," disclosed in U.S. Pat. No.
4,530,353, is manufactured from a sheet of heat fusible fibrous
material, such as a nonwoven batt, which is folded at the center
into a 3-layer pad and calendered at the sides to form tabs. The
pad is then provided with a wound release surface, the tabs are
coated with a hot melt adhesive and the bandage as a whole is
fitted with release strips.
Unfortunately, the resulting product--like its predecessor
disposable bandages--introduces fibrous batt type fibers and lint
into the area of the wound, provides calendered adhesive coated
thermoplastic tabs having no apparent absorbency or moisture vapor
permeability, and covers the area of the wound with a comparatively
non-resilient fibrous batt material. Furthermore, only the tab
portions of the bandage may be coated with the hot melt adhesive,
necessitating careful application of the adhesive to specified
portions of the bandage during manufacture. In addition, the
manufacture of the bandage requires both the preparation of a
triple fold in the batt material and the precise calendering of the
bandage--before application of the adhesive--to heat seal both the
tab portions of the bandage and a tiny section of each side of the
folded pad. Without this precise calendering, the structural
integrity of the bandage might be well be lost during manufacture,
marketing or use.
In view of all of the patented or otherwise known bandage products
and designs, therefore, a need remains for an improved disposable
bandage which may be manufactured from a single flat sheet, without
folding, may be fabricated without gauze, batts, or other fibrous
linting materials, and may be coated with a single adhesive layer
over its entire surface, for ease of manufacture. Such a product
would additionally demonstrate improved absorbency over known
fibrous materials, as well as superior protective resilience in the
area of the wound and ready permeability to moisture and moisture
vapor in both the pad area and the adhesive tabs of the
bandage.
BRIEF DESCRIPTION OF THE INVENTION
As an article to meet these needs, the present invention is a
disposable bandage, and a process for manufacturing it, which is
prepared from a single sheet or strip of liquid permeable,
flexible, hydrophilic thermoplastic foam. The process includes
coating the entire surface of one side of a foam sheet or strip
with a layer of porous pressure sensitive adhesive, positioning
wound release material in the area(s) of the sheet or strip
intended for wound contact, covering the same side of the laminate
in entirety with a suitable release liner and heat compressing the
laminate except in the area of the pad. Numerous foam bandages may
be prepared from the same sheet of foam by cutting the selectively
heat compressed laminate into individual bandages. The foam bandage
so produced provides both a resilient absorbent pad and thin but
absorbent adhesive-coated tabs. Furthermore, the single layer of
porous pressure sensitive adhesive adheres the wound release
material to the pad during and after manufacture, adheres the tabs
to the skin during use, and permits the ready passage of fluid
(i.e., water, serum, wound exudate, or moisture) or moisture vapor
into the absorbent areas of the bandage. Optionally, the bandage
may be prepared from a foam sheet having a moisture vapor
permeable, moisture impermeable skin thereon, or a similar skin may
be cast onto the prepared bandage; in either case, the skin
provides a water- and bacteria-proof protective outer layer for the
foam bandage described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a perspective view of the foam bandage 10,
having a pad 20, first and second tabs 22 and 24, and release
strips 52 and 54 thereon; and
FIG. 2 illustrates a side elevational view of the pad 20, having
layers of porous pressure sensitive adhesive 26 and wound release
material 28 laminated thereto beneath the release strips 52 and
54.
DETAILED DESCRIPTION OF THE INVENTION
As described above, the process for preparing the present foam
bandage includes coating one side of a polyurethane foam sheet with
a layer of porous pressure sensitive adhesive, positioning wound
release material and release liner adjacent the adhesive, and heat
compressing the entire laminate except in the area(s) of the
wound-covering pad(s). The equipment and methods for accomplishing
these laminating steps are well-known in the art, as explained
below. The selection of the particular materials for incorporation
in the laminate and the resultant foam bandage requires special
care, however, and so the foam bandage is best described by
identifying first those component materials suitable for use
therein.
I. Liquid Permeable, Flexible Foams
The liquid permeable, flexible foams suitable for use in the
present invention are those which demonstrate significant, and
preferably substantial, hydrophilicity. These hydrophilic
compositions may be prepared by any means known in the art, i.e.,
foaming prepolymers by means of the addition of chemical or
physical blowing agents. Accordingly, hydrophilic polyurethane
compositions may be prepared either by foaming isocyanate-capped
prepolymers by the addition of water, or by frothing aqueous
dispersion of fully reacted polyurethane polymers to entrap
chemically inert gases therein. These foam compositions must be
prepared, of course, with the understanding that any types or
amounts of additives, introduced to confer or improve
hydrophilicity or other characteristics of the foam, will not
result in medically unacceptable cytoxicity in the ultimate
composition so produced. For example, the following surfactants may
be used to enhance hydrophilicity in the preparation of hydrophilic
foam compositions for use in the present invention: sorbitan
trioleate; polyoxyethylene sorbitan oleate; polyoxyethylene
sorbitan monolaureate; polyoxyethylene lauryl ether;
polyoxyethylene stearyl ether; fluorochemical surfactants such as
Zonyl FSN by E. I. du Pont and Fluorad FC 170C by 3M, and block
copolymer condensates of ethylene oxide and propylene oxide with
propylene glycol, such as the PLURONIC surfactants available from
BASF Wyandotte.
In addition, the compositions suitable for use in the present
invention are those which are thermoplastic, i.e., which reversibly
soften upon heating. Preferably, the compositions will soften and
become tacky, or at least self-adherent, between 225.degree. and
300.degree. F., although compositions may be used which soften
between 200.degree. and 350.degree. F. Accordingly, the
thermoplastic compositions incorporated into the invention
demonstrate thermal stability at ordinary room temperatures.
Finally, the foam compositions suitable for use in the present
invention are those which may be cast or skived into low-density
sheets. In particular, sheets formed from these compositions must
have a density between 4 and 20 lbs/ft.sup.3, preferably between 7
and 13 lbs/ft.sup.3, and more preferably between 10 and 12
lbs/ft.sup.3. The low density of the foam contributes both to the
lightweight absorbency of the foam bandage and the low cost of the
materials necessary in the manufacture thereof. The low density
foams may be open-celled or partially open-celled, as long as the
foams are liquid permeable in contrast to the rigid impermeable
closed-cell foams.
The most widely available foams for the purpose of the present
invention are the polyurethanes, including those which result from
foaming isocyanate-capped prepolymers and those prepared by
frothing aqueous polyurethane dispersions. For the purpose of the
present invention, however, foam sheets prepared by mechanically
frothing, casting and curing aqueous polyurethane dispersions are
preferred. The polyurethanes having utility for this preferred
purpose are, accordingly, those recognized in the art as ionically
water dispersible. These dispersions are in contrast with the
emulsified isocyanate copolymers such as those disclosed in U.S.
Pat. No. 2,968,575, which are prepared and dispersed in water with
the aid of detergents under the action of powerful shearing forces.
The emulsified polyurethanes have the disadvantage that a detergent
must be used to form the emulsion and such detergent is usually
retained in the cured polyurethane, thus seriously detracting from
the overall physical and chemical properties of the final
product.
The preferred system for preparing aqueous ionic polyurethane
dispersions is to prepare polymers that have free acid groups,
preferably carboxylic acid groups, covalently bonded to the polymer
backbone. Neutralization of these carboxyl groups with an amine,
preferably a water soluble mono-amine, affords water dilutability.
Careful selection of the compound bearing the carboxylic group must
be made because isocyanates, the reactive group employed most often
in the generation of urethane linkages, are generally reactive with
carboxylic groups. However, as disclosed in U.S. Pat. No.
3,412,054, incorporated herein by reference,
2,2-hydroxymethyl-substituted carboxylic acids can be reacted with
organic polyisocyanates without significant reaction between the
acid and isocyanate groups as a result of the steric hindrance of
the carboxyl by the adjacent alkyl groups. This approach provides
the desired carboxy-containing polymer with the carboxylic groups
being neutralized with the tertiary mono-amine to provide an
internal quaternary ammonium salt and, hence, water
dilutability.
Suitable carboxylic acids and, preferably, the sterically hindered
carboxylic acids, are well-known and readily available. For
example, they may be prepared from an aldehyde that contains at
least two hydrogens in the alpha position which are reacted in the
presence of a base with two equivalents of formaldehyde to form a
2,2-hydroxymethyl aldehyde. The aldehyde is then oxidized to the
acid by procedures known to those skilled in the art. Such acids
are represented by the structural formula: ##STR1## wherein R
represents hydrogen, or alkyl of up to 20 carbon atoms, and
preferably, up to 8 carbon atoms. A preferred acid is
2,2-di(hydroxymethyl)propionic acid.
The polymers with the pendant carboxyl groups are characterized as
anionic polyurethane polymers. Further in accordance with the
present invention, however, an alternate route to confer water
dilutability is to use a cationic polyurethane having pendant amino
groups. Such cationic polyurethanes are disclosed in U.S. Pat. No.
4,066,591, incorporated herein by reference, and particularly, in
Example XVIII. In the context of the present invention, however,
anionic polyurethane dispersions are preferred.
The polyurethanes useful in the practice of the invention more
particularly involve the reaction of di- or polyisocyanates and
compounds with multiple reactive hydrogens suitable for the
preparation of polyurethanes. Such diisocyanates and reactive
hydrogen compounds are more fully disclosed in U.S. Pat. No.
3,412,054 and No. 4,046,729. Further, the processes to prepare such
polyurethanes are well recognized as exemplified by the
aforementioned patents. In accordance with the present invention,
therefore, aromatic, aliphatic and cyclo-aliphatic diisocyanates or
mixtures thereof can be used in forming the polymer. Such
diisocyanates, for example, are tolylene-2,4-diisocyanate;
tolylene-2,6-diisocyanate; meta-phenylene diisocyanate;
biphenylene-4,4'-diisocyanate; methylene-bis-(4-phenol isocyanate);
4,4-chloro-1,3-phenylene diisocyanate;
naphthylene-1,5-diisocyanate; tetramethylene-1,4-diisocyante;
hexamethylene-1,6-diisocyanate; decamethylene-1,10-diisocyanate;
cyclohexylene-1,4-diisocyanate; isophorone diisocyanate and the
like. Preferably, the arylene and cycloaliphatic diisocyanates are
used in the practice of the invention.
Characteristically, the arylene diisocyanates encompass those in
which the isocyanate group is attached to the aromatic ring. The
most preferred isocyanates are the 2,4 and 2,6 isomers of tolylene
diisocyanate and mixtures thereof, due to their reactivity and
ready availability. The cycloaliphatic diisocyanates used most
advantageously in the practice of the present invention are
4,4'-methylene-bis(cyclohexyl isocyanate) and isophorone
diisocyanate.
Selection of the aromatic or aliphatic diisocyanates is predicated
upon the final end use of the particular material. As is well
recognized by those skilled in the art, the aromatic isocyanates
may be used where the final product is not excessively exposed to
ultraviolet radiation, which tends to yellow such polymeric
compositions. The aliphatic diisocyanates, on the other hand, may
be more advantageously used in exterior applications and may have
less tendency to yellow upon exposure to ultraviolet radiation.
Although these principles form a general basis for the selection of
the particular isocyanate to be used, the aromatic diisocyanates
may be further stabilized by well-known ultraviolet stabilizers to
enhance the final properties of the polyurethane product. In
addition, antioxidants may be added in art recognized levels to
improve the characteristics of the final dispersions. Typical
antioxidants are the thioethers and phenolic antioxidants such as
4,4'-butylidine-bis-meta cresol and
2,6-ditert-butyl-para-cresol.
The isocyanate is reacted with the multiple reactive hydrogen
compounds such as diols, diamines or triols. In the case of diols
or triols, they are typically either polyalkylene ether or
polyester polyols. A polyalkylene ether polyol is the preferred
active hydrogen containing polymeric material for formulation of
the polyurethane. The most useful polyglycols have a molecular
weight of 50 to 10,000 and, in the context of the present
invention, the most preferred is from about 400 to about 7,000 with
the higher molecular weight polyols conferring proportionately
greater flexibility upon the polymer. The desired elastomeric
behavior will generally require approximately 0.5-80 percent by
weight of a long chain polyol (i.e. 700 to 2,000 eq. wt.) in the
polymer.
Examples of the polyether polyols are, but not limited to,
polyethylene ether glycol, polypropylene ether glycol,
polytetramethylene ether glycol, polyhexamethylene ether glycol,
polyoctamethylene ether glycol, polydecamethylene ether glycol,
polydodecamethylene ether glycol, and mixtures thereof. Polyglycols
containing several different radicals in the molecular chain, such
as, for example, the compound HO(CH.sub.2 OC.sub.2 H.sub.4 O).sub.n
H wherein n is an integer greater than 1, can also be used.
The polyol may also be a hydroxy terminated or hydroxy pendant
polyester which can be used instead of or in combination with the
polyalkylene ether glycols. Exemplary of such polyesters are those
formed by reacting acids, esters or acid halides with glycols.
Suitable glycols are polymethylene glycols, such as ethylene,
propylene, tetramethylene or decamethylene glycol; substituted
methylene glycols such as 2,2-dimethyl-1,3-propane diol, cyclic
glycols such as cyclohexane diol and aromatic glycols. Aliphatic
glycols are generally preferred when flexibility is desired. These
glycols are reacted with aliphatic, cycloaliphatic or aromatic
dicarboxylic acids or lower alkyl esters for ester-forming
derivatives to produce relatively low molecular weight polymers,
preferably having a melting point of less than about 70.degree. C.
and a molecular weight comparable to those set forth above for the
polyalkylene ether glycols. Acids suitable for use in preparing
such polyesters are, for example, phthalic, maleic, succinic,
adipic, suberic, sebacic, terephthalic and hexahydrophthalic acids
and the alkyl and halogen substituted derivatives of these acids.
In addition, a polycaprolactone terminated with hydroxyl groups may
also be used.
When used herein, "ionic dispersing agent" means an ionizable acid
or base capable of forming a salt with the solubilizing agent.
These "ionic dispersing agents" are amines and preferably are water
soluble amines such as triethylamine, tripropylamine, N-ethyl
piperidine, and the like; also, acid and preferably water soluble
acids such as acetic, propionic, lactic, and the like. Naturally,
an acid or amine will be selected contingent upon the solubilizing
group pendant on the polymer chain.
In forming the polyurethanes useful in the practice of the
invention, the polyol and a molar excess of diisocyanate are
reacted to form isocyanate terminated polymer. Although suitable
reaction conditions and reaction times and temperatures are
variable within the context of the particular isocyanate and polyol
utilized, those skilled in the art well recognize the variations.
Such skilled artisans recognize that reactivity of the ingredients
involved requires the balance of reaction rate with undesirable
secondary reactions leading to color and molecular weight
degradation. Typically, the reaction is carried out with stirring
at about 50.degree. C. to about 100.degree. C. for about 1 to 4
hours. To provide pendant carboxyl groups, the isocyanate
terminated polymer is reacted with a molar deficiency of dihydroxy
acid for 1 to 4 hours at 50.degree. C. to 120.degree. C., to form
isocyanate prepolymer. The acid is desirably added as a solution,
for example, in N-methyl-1,2-pyrrolidone or N-N-dimethylformamide.
The solvent for the acid will typically be no more than about 5
percent of the total charge in order to minimize the organic
solvent concentration in the polyurethane composition. After the
dihydroxy acid is reacted into the polymer chain, the pendant
carboxyl groups are neutralized with an amine at about
58.degree.-75.degree. C. for about 20 minutes, and chain extension
and dispersion are accomplished by addition to water with stirring.
A water soluble diamine may be added to the water as an additional
chain extender. The chain extension involves the reaction of the
remaining isocyanate groups with water to form urea groups and to
polymerize further the polymeric materials, with the result that
all the isocyanate groups are reacted by virtue of the addition to
a large stoichiometric excess of water.
The dispersion viscosity is generally in the range of from 10 to
1000 centipoise. Useful solutions of polyurethane in organic
solvents, by contrast, generally have viscosities of several
thousand centipoise, ranging as high as 50,000 centipoise when the
solution contains about 20 to 30 percent by weight
polyurethane.
Suitable polyurethane dispersions contain, moreover, about 50 to 75
percent by weight polyurethane solids in dispersion, said solids
preferably having a carboxyl content between about 92 and 98 meq
per each 100 grams thereof. The preferred polyurethane
concentration is 55 to 70 percent by weight and the most preferred
concentration is 65 percent by weight polyurethane solids in
dispersion.
Particle size, as a useful measure of stability, may be measured by
light scattering. Useful dispersions having non-settling
characteristics will have particles of a diameter of less than 5
microns.
Particularly useful polyurethane dispersions include the
non-crosslinked polyurethane compositions recited in U.S. Pat. No.
4,171,391, incorporated herein by reference. The polyurethane
dispersions most preferred for use in the present invention,
however, are those available from Witco Chemical Company under the
trade designation Witcobond.RTM. W-290H; these dispersions yield
foams which demonstrate inherent hydrophilicity, even in the
absence of surfactants. The Witcobond.RTM. W290H dispersions
contain 65 percent by weight anionic polyurethane solids having
particulate diameters less than 5 microns.
In order to froth the aqueous ionic polyurethane dispersions in
accordance with the present invention, the dispersions are first
admixed with a stearic acid salt and a small amount of an aziridine
crosslinking agent. The salt of stearic acid may be selected from
the group consisting of aluminum stearate, ammonium stearate,
calcium stearate, potassium stearate and sodium stearate. The
aziridine crosslinking agent may be any known aziridine
crosslinking agent wherein the agent has monofunctional or
polyfunctional aziridine activity due to the incorporation therein
of ethyleneimine, propyleneimine, butyleneimine or derivatives
thereof. Preferably, the aziridine selected is the polyfunctional
aziridine preparation of proprietary formula, sold under the
trademark XAMA.RTM.-7, which contains 6.35 to 6.95 meq/g aziridine
content and has an aziridine functionality of approximately 3.3.
The XAMA.RTM.-7 polyfunctional aziridine has a viscosity of 1200 to
2000 centipoise at 25.degree. C., further has a density of 1.185
g/cc at 25.degree. C., and is completely miscible with water,
acetone, methanol, chloroform and benzene.
The admixture is prepared by combining between 80 and 120 parts by
weight of an aqueous ionic polyurethane dispersion, prepared as
described above, with between 0.5 to 1.5 parts by weight of
XAMA.RTM.-7 polyfunctional aziridine and between 1 and 9 parts by
weight of a 33 percent aqueous or nonaqueous dispersion of the
stearate salt. Different amounts and concentrations of other
stearate and aziridine preparations may be substituted in reactive
equivalent amounts. To this admixture may be added additional
ingredients and reactive or nonreactive additives, such as
surfactants, as desired.
On a laboratory scale, the dispersion, stearate and aziridine may
be admixed in a Hobar mixer; an Oaks or other industrial frothing
mixer is suitable for full scale production. After initial admixing
of the polyurethane dispersion, the stearate and the aziridine, the
mixture is frothed, by agitation and/or inert gas injection, to
yield a frothed admixture which has very fine, uniform bubbles and
which is suitable for immediately casting and curing. Although the
froth may be cast by other means, the froth is particularly suited
to the knife-casting techniques for preparing foam sheet materials.
Preferably, therefore, the liquid froth is cast upon a release
surface, such as silicone coated release paper, and coated to the
desired thickness with, for example, a Gardner knife. The release
paper-frothed layer is then passed through an oven to dry and cure
the foam. Temperatures of 225.degree. F. to 275.degree. F. are
suitable for drying and curing the foam, and the limited inclusion
of the aziridine compound ensures the thermoplasticity of the foam
sheet subsequent to curing.
II. Adhesives
A number of adhesive compositions are suitable for use in the
present invention. The adhesive must be, however, film-forming,
noncytotoxic within medically acceptable limits, and porous in its
ultimate film form. (The term "porous" signifies the presence of a
plurality of discontinuities or apertures.) Suitable adhesive
preparations therefore include, for example, solutions or emulsions
of acrylic adhesive resin, blends of butadiene-acrylonitrile
copolymers with resins such as oil-soluble, heat-hardening
phenol-formaldehyde resins, two-step thermosetting phenolic resin
compositions, coumarone-indene resins, polyterpine resins and the
like; polychloroprene combined with heat-hardening
phenol-formaldehyde resins, rosin-phenol resins, vinyl alkyl ether
polymer based adhesives, thermoplastic styrene-butadiene block
polymer rubbers mixed with resins such as those described, and
other such adhesive compositions.
Porosity may be conferred upon these adhesive compositions by means
known in the art. For example, a solution of the adhesive may be
frothed in a Hobart or Oakes mixer, followed by the casting and
curing of the resultant froth to yield a porous film. Because the
solvent removal necessary with conventional solvent systems
ordinarily creates problems of compliance with environmental safety
regulations, however, porous adhesive films prepared from aqueous
dispersions or emulsions of dispersible adhesive resins are popular
in the industry and are preferred for use in the present invention.
These dispersions or emulsions are frothed, cast and cured, in the
same manner as the solvent system adhesives to yield porous
pressure sensitive adhesive films. These films are adequately
porous as long as they are readily permeable, i.e., penetrable
within 90 seconds, to liquid water, serum, and ordinary wound
exudates.
Particularly useful pressure sensitive adhesive emulsions include
those sold in association with the mark Rhoplex.RTM., by Rohm and
Haas Company. These Rhoplex.RTM. adhesives includes Rhoplex N-560,
Rhoplex N-580, Rhoplex N-582, Rhoplex N-619, Rhoplex N-1031 and
Rhoplex LC-67. These preparations are particularly well suited to
the preparation of the present adhesive films because, for example,
they require no additional tackifying resins and yield films having
excellent resistance to delamination under wet conditions. In
addition, porous films prepared from these adhesive emulsions do
not lose tack or porosity under the application of heat, i.e., up
to 400.degree. F. Other adhesive films may accordingly be
substituted for the films prepared from the Rhoplex emulsions, as
long as the films do not lose tack or porosity at temperatures up
to and including 400.degree. F.
III. Structure, Function and Manufacture
Referring now to the drawings, and initially to FIG. 1, two or more
of the above-described polyurethane foams and adhesive formulations
are incorporated into tue preferred embodiment of the foam bandage
10 having a pad 20, a first tab 22 and a second tab 24, which are
backed, respectively, by the first and second release strips 52 and
54.
Referring now to FIG. 2, the porous pressure sensitive adhesive
layer 26 extends the length of the foam bandage 10, and is shown
adjacent to the foam layer of both the pad 20 and the first and
second tabs 22 and 24. A wound release liner layer 28 adheres to
the adhesive layer 26 in the area of the pad 20, and the first and
second release strips 52, 54 cover the entire bandage, contacting
the adhesive layer 26 only in the areas of the first and second
tabs 22 and 24. A moisture vapor permeable skin 30, which is
moisture vapor permeable yet moisture and bacteria impermeable, is
illustrated on the external surface of the foam bandage 10.
The preferred embodiment of the foam bandage, as illustrated in the
FIGS., functions generally as do other disposable bandages, and is
applied to the skin in the conventional manner. The pad 20 does not
lint, however, when brought adjacent an irritation or wound, and
the sole porous pressure sensitive adhesive layer 26 ensures gentle
adherence of the foam bandage to the skin during use. Furthermore,
both the first and second tabs 22 and 24 and the pad 20 are
constructed in part of a liquid permeable, flexible hydrophilic
polyurethane foam, and the tabs and the pad therefore both provide
ready absorption and transfer of fluids and moisture vapor from the
area of the wound or irritation. The moisture permeable hydrophilic
foam tabs 22, 24, exclusive of the moisture vapor permeable skin 30
thereon, furthermore tend to wick fluids away from the pad 20 when
the pad approaches saturation prior to the tabs. Moreover, the
ready transfer of moisture vapor though the foam bandage 10 remains
unaffected even when the bandage is wrapped and overlapped, i.e.,
around a finger, because the overlapped moisture vapor permeable
layers continue to define a moisture vapor permeable structure.
Accordingly, the moisture vapor permeable skin 30 provides a
bacterial barrier for the wound without causing skin maceration on
the otherwise moisture and moisture vapor permeable foam bandage
10.
The foam bandage according to the preferred and alternate
embodiments of the invention may be manufactured in a number of
ways, each of which is simple, straightforward and cost effective.
A low-density liquid permeable, flexible polyurethane foam sheet is
first prepared as described above. The porous pressure sensitive
adhesive layer is then adhered to the foam sheet by direct casting,
reverse-roll, transfer coating or other methods known in the art. A
wound release inner layer is then positioned in those areas of the
foam sheet/adhesive film laminate that are intended for wound
contact, i.e., pad areas. These wound release materials include the
Delnet.RTM. (Hercules) and Cerex.TM. (DuPont) materials and are
net-like, nonabsorbent materials which permit free passage of
fluids. (Delnet.RTM. wound release material, in particular, is a
high density perforated polyethylene sheet material which has good
adherence to pressure sensitive adhesive resins but functions as a
release surface to coagulated serum.) The resulting laminate, in
which wound release material is present only in the areas intended
for wound contact, accordingly contains three layers which
individually and collectively permit the free passage and
absorption of fluids, serum and wound exudate.
Over the entire foam/adhesive film/wound release liner layer is
then positioned a suitable release material. These release
materials include release papers known in the art along with any
other sheet materials having a release coating on one side thereof.
Typical release papers are prepared by slightly impregnating and
completely coating the surface of the paper or other material with
a composition which resists the adhesion of ordinary adhesives. A
number of such release coatings are known in the art, among them
being cured silicones, cured blends of alkyd resins and
urea-formaldehyde resins and stearato chromic chloride (e.q.,
"Quilon"). The release material may be positioned solely over the
adhesive areas free from wound release material or may be
overlapped across the designated pad area of the bandage in the
characteristic configuration typical of prior art disposable
bandages.
The resultant laminate is then heat compressed in those areas of
the laminate intended as the first and second tabs 22, 24; the
intended area of the pad 20 is left uncompressed. This heat
compression is preferably effected by heated rollers. If the
laminate is first cut into strips having a width the intended
length of each individual bandage, the side portions of each strip
may be heat compressed with smooth heated rollers; if the entire
sheet is heat compressed at once, a heated roller having a grid
pattern thereon corresponding to the desired bandage structure is
used. The rollers are heated to between 200.degree. and 350.degree.
F., and preferably are heated to between 225.degree. and
300.degree. F. If desired, only one of two cooperating rollers need
be heated, or a single heated roller may substitute for two
cooperating rollers under suitable manufacturing conditions. In any
event, the heat compression should proceed to heat compress the
laminate to a predetermined thickness by adjusting one or more
rollers to the corresponding gap, allowing for any shrinkage in the
heat-compressed polymer as it cures. Within the scope of this
invention, the foam/adhesive film/wound release layer/release liner
laminate may be heat compressed to any thickness as long as the
compressed portions of the laminate remain both moisture and
moisture vapor permeable. Preferably, however, the compressed
portions of the foam/adhesive film laminate will have less than the
thickness, and more preferably less than half of the thickness, of
the uncompressed pad areas thereof.
Optional elements may be added to the subject foam bandage without
altering the nature of the invention. First, the thermoplastic foam
may have a moisture vapor permeable, moisture impermeable skin,
such as a urethane skin, on the outside thereof, as is present in
the preferred embodiment of the invention; this urethane skin
opposes the wound release material and porous adhesive layers
intended for contact with the human skin surface. The moisture
vapor permeable, moisture impermeable skin may either be cast onto
the foam sheet or the ultimate prepared foam bandage, or may be
prepared as a substrate onto which the thermoplastic foam is
initially cast and cured. Second, additional optional absorbent
materials may be positioned between the porous pressure sensitive
adhesive layer and the wound release material in the area of the
pad by, for example, interposing a non-linting cellulose or other
absorbent layer narrower than the foam pad between the porous
pressure sensitive adhesive layer and the wound release material.
As a result, the entire absorbent layer and the edges of the wound
release material layer are affixed to the thermoplastic foam by
means of one layer of porous pressure sensitive adhesive. Unlike
the optional outer moisture vapor permeable skin of the foam
bandage, of course, this optional absorbent material must be
positioned within the laminate prior to the positioning of the
wound release material and release liners, and before the heat
compression of the assembled laminate.
Following heat compression, the laminate is permitted to cool, at
which time the thermoplastic foam either reverts to a stable solid
or becomes thermoset by the further heat activation of a
crosslinking compound (i.e., remaining unreacted aziridine) present
in the foam. After cooling, the laminate is cut into individual
disposable foam bandages and the bandages are packaged and
sterilized by means known in the art.
Bandage dimensions and thicknesses may be adjusted to suit specific
applications. Both strip- and island-type bandages may be prepared
in accordance with the present invention. Likewise, larger
disposable bandages in the configuration of general medical or
surgical dressings may be prepared and used in home-health or
hospital care of more serious wounds and conditions. The
hydrophilicity of the thermoplastic polyurethane foam, and the ease
of manufacture of the foam bandage as a whole, make it suitable and
cost effective for use in all first-aid, medical or surgical
applications.
The following Examples are illustrative of the foam bandage of the
present invention, and the process for preparing it.
EXAMPLE I
Five hundred parts by weight of Witcobond.RTM. W-290H aqueous
polyurethane dispersion, containing 62 percent by weight anionic
polyurethane solids, were admixed, at slow speed in a Hobart mixer,
with 25 parts by weight 33 percent aqueous ammonium stearate, five
parts by weight XAMA.RTM.-7 polyfunctional aziridine, fifteen parts
by weight Lexaine C (a cocamidopropyl betaine viscosity builder
available from Inolex Chemical Co., Philadelphia, Pa.) and 25 parts
by weight of Pluronic.RTM. L-62 surfactant. The resulting admixture
demonstrated a viscosity of 3000 centipoise.
The above admixture was mixed in the Hobart mixer for 1 minute at
low speed, 1 minute at medium speed, 2 minutes 30 seconds at high
speed and 2 minutes at low speed. The admixture thus frothed was
then coated, at 0.170" gap, over a 1 mil thick cured urethane skin
which demonstrated a moisture vapor transmission rate of 800
g/m.sup.2 /24 hours. The cast foam/urethane skin so produced was
cured by a 10 minute application of heat in a 250.degree. F. oven.
The resulting foam layer had a thickness of 110 mils and was firmly
adhered to the 1 mil thick urethane skin.
EXAMPLE II
A porous pressure sensitive adhesive film was prepared by admixing
50 parts by weight Rhoplex.RTM. N-560 pressure sensitive adhesive
emulsion and 50 parts by weight Rhoplex.RTM. N-580 pressure
sensitive adhesive emulsion. The admixed emulsions were frothed in
a Hobart mixer for 2 minutes at low speed, 2 minutes at medium
speed, and 3 minutes 30 seconds at high speed. The resultant
frothed emulsions were cast, using a Gardner knife set at 0.002",
onto silicone resin coated release paper. The cast adhesive was
dried into a film by heating for 8 minutes in a 300.degree. F.
oven. Samples of the porous pressure sensitive adhesive film
demonstrated ready permeability both to liquid water and to a
simulated serum containing water, electrolytes and albumin. The
porous pressure sensitive adhesive film so produced measured 1.5
mils in thickness.
EXAMPLE III
A sheet of the urethane skin/polyurethane foam laminate of Example
I was laminated, by its foam side, to a porous adhesive sheet
prepared in accordance with Example II; lamination was accomplished
by the adhesive transfer method. The resulting laminate was placed,
adhesive layer up, on a large horizontal work surface and the
release paper was removed. Leaving a one-inch margin on two
opposing sides of the laminate, one inch wide strips of Delnet.RTM.
wound release material were placed lengthwise along the entire
width of the sheet, with two inch spaces between each strip. Two
inch wide strips of silicone resin coated release paper were then
positioned along the entire width of the sheet, resting atop both
the adhesive and wound release material layers. The first two inch
wide strip was positioned at the left edge of the sheet, and the
second strip placed to overlap the first two inch strip by one
inch. The third two inch strip was positioned immediately adjacent
to--but not overlapping--the second strip and the fourth strip
overlapped the third by one inch. This process continued until the
entire skin/foam/adhesive film laminate was covered with
alternately overlapped strips of release paper. The laminate thus
covered was run through smooth hard rubber rollers, at room
temperature, to bond the layers into a cohesive sheet.
The resultant sheet was then cut into strips at each line of the
sheet along which the release paper did not overlap. A plurality of
laminated strips resulted, each of which had a width of three
inches and a central area of overlapped release paper measuring one
inch wide. Two sets of two cooperating one inch wide steel rollers
were heated to 250.degree. F. and were positioned parallel each
other, one inch apart. The cooperating rollers were each adjusted
to a 15 mil gap. The laminated strips were then passed through the
set of four rollers at a rate which permitted a dwell time of six
seconds. The sides of the laminated strip were accordingly heat
compressed into approximately a 15 mil thickness. The strips were
cooled at room temperature for 30 minutes and were then sliced into
individual foam bandages having the appearance of the foam bandage
illustrated in FIG. 1.
Although the invention has been described with reference to
specific materials and specific processes, the invention is to be
limited only insofar as is set forth in the accompanying
claims.
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